A conventional synchronous motor control device disclosed in Patent Literature 1 sets a positioning mode and a synchronous operation mode subsequent to the positioning mode. In the positioning mode, a gradually increasing direct current is supplied to an armature winding of a permanent magnet synchronous motor at startup of the permanent magnet synchronous motor. In the synchronous operation mode, an alternating current with variable voltage and variable frequency is supplied to the armature winding. The synchronous motor control in the positioning mode device detects a current value flowing through the armature winding of the permanent magnet synchronous motor, and, when the current value is smaller than or equal to a preset threshold, determines that the permanent magnet synchronous motor is not connected to the synchronous motor control device and then generates an alarm.